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 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.io;

/**
 * The {@code DataInput} interface provides
 * for reading bytes from a binary stream and
 * reconstructing from them data in any of
 * the Java primitive types. There is also
 * a
 * facility for reconstructing a {@code String}
 * from data in
 * <a href="#modified-utf-8">modified UTF-8</a>
 * format.
 * <p>
 * It is generally true of all the reading
 * routines in this interface that if end of
 * file is reached before the desired number
 * of bytes has been read, an {@code EOFException}
 * (which is a kind of {@code IOException})
 * is thrown. If any byte cannot be read for
 * any reason other than end of file, an {@code IOException}
 * other than {@code EOFException} is
 * thrown. In particular, an {@code IOException}
 * may be thrown if the input stream has been
 * closed.
 *
 * <h3><a name="modified-utf-8">Modified UTF-8</a></h3>
 * <p>
 * Implementations of the DataInput and DataOutput interfaces represent
 * Unicode strings in a format that is a slight modification of UTF-8.
 * (For information regarding the standard UTF-8 format, see section
 * <i>3.9 Unicode Encoding Forms</i> of <i>The Unicode Standard, Version
 * 4.0</i>).
 * Note that in the following table, the most significant bit appears in the
 * far left-hand column.
 *
 * <blockquote>
 * <table border="1" cellspacing="0" cellpadding="8"
 * summary="Bit values and bytes">
 * <tr>
 * <th colspan="9"><span style="font-weight:normal">
 * All characters in the range {@code '\u005Cu0001'} to
 * {@code '\u005Cu007F'} are represented by a single byte:</span></th>
 * </tr>
 * <tr>
 * <td></td>
 * <th colspan="8" id="bit_a">Bit Values</th>
 * </tr>
 * <tr>
 * <th id="byte1_a">Byte 1</th>
 * <td><center>0</center>
 * <td colspan="7"><center>bits 6-0</center>
 * </tr>
 * <tr>
 * <th colspan="9"><span style="font-weight:normal">
 * The null character {@code '\u005Cu0000'} and characters
 * in the range {@code '\u005Cu0080'} to {@code '\u005Cu07FF'} are
 * represented by a pair of bytes:</span></th>
 * </tr>
 * <tr>
 * <td></td>
 * <th colspan="8" id="bit_b">Bit Values</th>
 * </tr>
 * <tr>
 * <th id="byte1_b">Byte 1</th>
 * <td><center>1</center>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="5"><center>bits 10-6</center>
 * </tr>
 * <tr>
 * <th id="byte2_a">Byte 2</th>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="6"><center>bits 5-0</center>
 * </tr>
 * <tr>
 * <th colspan="9"><span style="font-weight:normal">
 * {@code char} values in the range {@code '\u005Cu0800'}
 * to {@code '\u005CuFFFF'} are represented by three bytes:</span></th>
 * </tr>
 * <tr>
 * <td></td>
 * <th colspan="8"id="bit_c">Bit Values</th>
 * </tr>
 * <tr>
 * <th id="byte1_c">Byte 1</th>
 * <td><center>1</center>
 * <td><center>1</center>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="4"><center>bits 15-12</center>
 * </tr>
 * <tr>
 * <th id="byte2_b">Byte 2</th>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="6"><center>bits 11-6</center>
 * </tr>
 * <tr>
 * <th id="byte3">Byte 3</th>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="6"><center>bits 5-0</center>
 * </tr>
 * </table>
 * </blockquote>
 * <p>
 * The differences between this format and the
 * standard UTF-8 format are the following:
 * <ul>
 * <li>The null byte {@code '\u005Cu0000'} is encoded in 2-byte format
 * rather than 1-byte, so that the encoded strings never have
 * embedded nulls.
 * <li>Only the 1-byte, 2-byte, and 3-byte formats are used.
 * <li><a href="../lang/Character.html#unicode">Supplementary characters</a>
 * are represented in the form of surrogate pairs.
 * </ul>
 *
 * @author Frank Yellin
 * @see java.io.DataInputStream
 * @see java.io.DataOutput
 * @since JDK1.0
 */
public interface DataInput {

  /**
   * Reads some bytes from an input
   * stream and stores them into the buffer
   * array {@code b}. The number of bytes
   * read is equal
   * to the length of {@code b}.
   * <p>
   * This method blocks until one of the
   * following conditions occurs:
   * <ul>
   * <li>{@code b.length}
   * bytes of input data are available, in which
   * case a normal return is made.
   *
   * <li>End of
   * file is detected, in which case an {@code EOFException}
   * is thrown.
   *
   * <li>An I/O error occurs, in
   * which case an {@code IOException} other
   * than {@code EOFException} is thrown.
   * </ul>
   * <p>
   * If {@code b} is {@code null},
   * a {@code NullPointerException} is thrown.
   * If {@code b.length} is zero, then
   * no bytes are read. Otherwise, the first
   * byte read is stored into element {@code b[0]},
   * the next one into {@code b[1]}, and
   * so on.
   * If an exception is thrown from
   * this method, then it may be that some but
   * not all bytes of {@code b} have been
   * updated with data from the input stream.
   *
   * @param b the buffer into which the data is read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  void readFully(byte b[]) throws IOException;

  /**
   * Reads {@code len}
   * bytes from
   * an input stream.
   * <p>
   * This method
   * blocks until one of the following conditions
   * occurs:
   * <ul>
   * <li>{@code len} bytes
   * of input data are available, in which case
   * a normal return is made.
   *
   * <li>End of file
   * is detected, in which case an {@code EOFException}
   * is thrown.
   *
   * <li>An I/O error occurs, in
   * which case an {@code IOException} other
   * than {@code EOFException} is thrown.
   * </ul>
   * <p>
   * If {@code b} is {@code null},
   * a {@code NullPointerException} is thrown.
   * If {@code off} is negative, or {@code len}
   * is negative, or {@code off+len} is
   * greater than the length of the array {@code b},
   * then an {@code IndexOutOfBoundsException}
   * is thrown.
   * If {@code len} is zero,
   * then no bytes are read. Otherwise, the first
   * byte read is stored into element {@code b[off]},
   * the next one into {@code b[off+1]},
   * and so on. The number of bytes read is,
   * at most, equal to {@code len}.
   *
   * @param b the buffer into which the data is read.
   * @param off an int specifying the offset into the data.
   * @param len an int specifying the number of bytes to read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  void readFully(byte b[], int off, int len) throws IOException;

  /**
   * Makes an attempt to skip over
   * {@code n} bytes
   * of data from the input
   * stream, discarding the skipped bytes. However,
   * it may skip
   * over some smaller number of
   * bytes, possibly zero. This may result from
   * any of a
   * number of conditions; reaching
   * end of file before {@code n} bytes
   * have been skipped is
   * only one possibility.
   * This method never throws an {@code EOFException}.
   * The actual
   * number of bytes skipped is returned.
   *
   * @param n the number of bytes to be skipped.
   * @return the number of bytes actually skipped.
   * @throws IOException if an I/O error occurs.
   */
  int skipBytes(int n) throws IOException;

  /**
   * Reads one input byte and returns
   * {@code true} if that byte is nonzero,
   * {@code false} if that byte is zero.
   * This method is suitable for reading
   * the byte written by the {@code writeBoolean}
   * method of interface {@code DataOutput}.
   *
   * @return the {@code boolean} value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  boolean readBoolean() throws IOException;

  /**
   * Reads and returns one input byte.
   * The byte is treated as a signed value in
   * the range {@code -128} through {@code 127},
   * inclusive.
   * This method is suitable for
   * reading the byte written by the {@code writeByte}
   * method of interface {@code DataOutput}.
   *
   * @return the 8-bit value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  byte readByte() throws IOException;

  /**
   * Reads one input byte, zero-extends
   * it to type {@code int}, and returns
   * the result, which is therefore in the range
   * {@code 0}
   * through {@code 255}.
   * This method is suitable for reading
   * the byte written by the {@code writeByte}
   * method of interface {@code DataOutput}
   * if the argument to {@code writeByte}
   * was intended to be a value in the range
   * {@code 0} through {@code 255}.
   *
   * @return the unsigned 8-bit value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  int readUnsignedByte() throws IOException;

  /**
   * Reads two input bytes and returns
   * a {@code short} value. Let {@code a}
   * be the first byte read and {@code b}
   * be the second byte. The value
   * returned
   * is:
   * <pre>{@code (short)((a << 8) | (b & 0xff))
   * }</pre>
   * This method
   * is suitable for reading the bytes written
   * by the {@code writeShort} method of
   * interface {@code DataOutput}.
   *
   * @return the 16-bit value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  short readShort() throws IOException;

  /**
   * Reads two input bytes and returns
   * an {@code int} value in the range {@code 0}
   * through {@code 65535}. Let {@code a}
   * be the first byte read and
   * {@code b}
   * be the second byte. The value returned is:
   * <pre>{@code (((a & 0xff) << 8) | (b & 0xff))
   * }</pre>
   * This method is suitable for reading the bytes
   * written by the {@code writeShort} method
   * of interface {@code DataOutput}  if
   * the argument to {@code writeShort}
   * was intended to be a value in the range
   * {@code 0} through {@code 65535}.
   *
   * @return the unsigned 16-bit value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  int readUnsignedShort() throws IOException;

  /**
   * Reads two input bytes and returns a {@code char} value.
   * Let {@code a}
   * be the first byte read and {@code b}
   * be the second byte. The value
   * returned is:
   * <pre>{@code (char)((a << 8) | (b & 0xff))
   * }</pre>
   * This method
   * is suitable for reading bytes written by
   * the {@code writeChar} method of interface
   * {@code DataOutput}.
   *
   * @return the {@code char} value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  char readChar() throws IOException;

  /**
   * Reads four input bytes and returns an
   * {@code int} value. Let {@code a-d}
   * be the first through fourth bytes read. The value returned is:
   * <pre>{@code
   * (((a & 0xff) << 24) | ((b & 0xff) << 16) |
   *  ((c & 0xff) <<  8) | (d & 0xff))
   * }</pre>
   * This method is suitable
   * for reading bytes written by the {@code writeInt}
   * method of interface {@code DataOutput}.
   *
   * @return the {@code int} value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  int readInt() throws IOException;

  /**
   * Reads eight input bytes and returns
   * a {@code long} value. Let {@code a-h}
   * be the first through eighth bytes read.
   * The value returned is:
   * <pre>{@code
   * (((long)(a & 0xff) << 56) |
   *  ((long)(b & 0xff) << 48) |
   *  ((long)(c & 0xff) << 40) |
   *  ((long)(d & 0xff) << 32) |
   *  ((long)(e & 0xff) << 24) |
   *  ((long)(f & 0xff) << 16) |
   *  ((long)(g & 0xff) <<  8) |
   *  ((long)(h & 0xff)))
   * }</pre>
   * <p>
   * This method is suitable
   * for reading bytes written by the {@code writeLong}
   * method of interface {@code DataOutput}.
   *
   * @return the {@code long} value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  long readLong() throws IOException;

  /**
   * Reads four input bytes and returns
   * a {@code float} value. It does this
   * by first constructing an {@code int}
   * value in exactly the manner
   * of the {@code readInt}
   * method, then converting this {@code int}
   * value to a {@code float} in
   * exactly the manner of the method {@code Float.intBitsToFloat}.
   * This method is suitable for reading
   * bytes written by the {@code writeFloat}
   * method of interface {@code DataOutput}.
   *
   * @return the {@code float} value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  float readFloat() throws IOException;

  /**
   * Reads eight input bytes and returns
   * a {@code double} value. It does this
   * by first constructing a {@code long}
   * value in exactly the manner
   * of the {@code readLong}
   * method, then converting this {@code long}
   * value to a {@code double} in exactly
   * the manner of the method {@code Double.longBitsToDouble}.
   * This method is suitable for reading
   * bytes written by the {@code writeDouble}
   * method of interface {@code DataOutput}.
   *
   * @return the {@code double} value read.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   */
  double readDouble() throws IOException;

  /**
   * Reads the next line of text from the input stream.
   * It reads successive bytes, converting
   * each byte separately into a character,
   * until it encounters a line terminator or
   * end of
   * file; the characters read are then
   * returned as a {@code String}. Note
   * that because this
   * method processes bytes,
   * it does not support input of the full Unicode
   * character set.
   * <p>
   * If end of file is encountered
   * before even one byte can be read, then {@code null}
   * is returned. Otherwise, each byte that is
   * read is converted to type {@code char}
   * by zero-extension. If the character {@code '\n'}
   * is encountered, it is discarded and reading
   * ceases. If the character {@code '\r'}
   * is encountered, it is discarded and, if
   * the following byte converts &#32;to the
   * character {@code '\n'}, then that is
   * discarded also; reading then ceases. If
   * end of file is encountered before either
   * of the characters {@code '\n'} and
   * {@code '\r'} is encountered, reading
   * ceases. Once reading has ceased, a {@code String}
   * is returned that contains all the characters
   * read and not discarded, taken in order.
   * Note that every character in this string
   * will have a value less than {@code \u005Cu0100},
   * that is, {@code (char)256}.
   *
   * @return the next line of text from the input stream, or {@code null} if the end of file is
   * encountered before a byte can be read.
   * @throws IOException if an I/O error occurs.
   */
  String readLine() throws IOException;

  /**
   * Reads in a string that has been encoded using a
   * <a href="#modified-utf-8">modified UTF-8</a>
   * format.
   * The general contract of {@code readUTF}
   * is that it reads a representation of a Unicode
   * character string encoded in modified
   * UTF-8 format; this string of characters
   * is then returned as a {@code String}.
   * <p>
   * First, two bytes are read and used to
   * construct an unsigned 16-bit integer in
   * exactly the manner of the {@code readUnsignedShort}
   * method . This integer value is called the
   * <i>UTF length</i> and specifies the number
   * of additional bytes to be read. These bytes
   * are then converted to characters by considering
   * them in groups. The length of each group
   * is computed from the value of the first
   * byte of the group. The byte following a
   * group, if any, is the first byte of the
   * next group.
   * <p>
   * If the first byte of a group
   * matches the bit pattern {@code 0xxxxxxx}
   * (where {@code x} means "may be {@code 0}
   * or {@code 1}"), then the group consists
   * of just that byte. The byte is zero-extended
   * to form a character.
   * <p>
   * If the first byte
   * of a group matches the bit pattern {@code 110xxxxx},
   * then the group consists of that byte {@code a}
   * and a second byte {@code b}. If there
   * is no byte {@code b} (because byte
   * {@code a} was the last of the bytes
   * to be read), or if byte {@code b} does
   * not match the bit pattern {@code 10xxxxxx},
   * then a {@code UTFDataFormatException}
   * is thrown. Otherwise, the group is converted
   * to the character:
   * <pre>{@code (char)(((a & 0x1F) << 6) | (b & 0x3F))
   * }</pre>
   * If the first byte of a group
   * matches the bit pattern {@code 1110xxxx},
   * then the group consists of that byte {@code a}
   * and two more bytes {@code b} and {@code c}.
   * If there is no byte {@code c} (because
   * byte {@code a} was one of the last
   * two of the bytes to be read), or either
   * byte {@code b} or byte {@code c}
   * does not match the bit pattern {@code 10xxxxxx},
   * then a {@code UTFDataFormatException}
   * is thrown. Otherwise, the group is converted
   * to the character:
   * <pre>{@code
   * (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
   * }</pre>
   * If the first byte of a group matches the
   * pattern {@code 1111xxxx} or the pattern
   * {@code 10xxxxxx}, then a {@code UTFDataFormatException}
   * is thrown.
   * <p>
   * If end of file is encountered
   * at any time during this entire process,
   * then an {@code EOFException} is thrown.
   * <p>
   * After every group has been converted to
   * a character by this process, the characters
   * are gathered, in the same order in which
   * their corresponding groups were read from
   * the input stream, to form a {@code String},
   * which is returned.
   * <p>
   * The {@code writeUTF}
   * method of interface {@code DataOutput}
   * may be used to write data that is suitable
   * for reading by this method.
   *
   * @return a Unicode string.
   * @throws EOFException if this stream reaches the end before reading all the bytes.
   * @throws IOException if an I/O error occurs.
   * @throws UTFDataFormatException if the bytes do not represent a valid modified UTF-8 encoding of
   * a string.
   */
  String readUTF() throws IOException;
}
